1. Field of the Invention
This invention relates generally to hose pull traveling sprinkler irrigation machines that use turbines as motive power therefor. Such machines employ various type systems to maintain proper speed and sprinkler action.
2. Description of the Prior Art
A common problem with existing traveling sprinklers is in the fact that the speed thereof must be varied in operation, and it has become common practice to bypass water around the turbine motive power system in order to achieve part of the speed control. Several inherent problems exist with this method of bypassing water around the turbine in order to control speed.
Many of the known prior art traveling sprinkler irrigation machines employ axial flow or propeller type turbines as their motive power. With this type of turbine attempting to control the speed of the turbine by bypassing water around the turbine results in very poor speed regulation, because with this type of turbine the pressure drop across the turbine is directly related to the load, such that as the load increases the pressure drop increases. This results in a greater percentage of the total flow bypassing the turbine when the load dictates that the greatest percentage of the flow should be passing through the turbine. Conversely, when the load is light, the pressure drop across the turbine is small, very little water is caused to pass through the bypass, and the turbine tends to run faster than required. Thus it can be seen that with this type of turbine drive, speed regulation is a great problem.
Another common known type of sprinkler machines employ radial or centrifugal type turbines which do have better results from bypassing water around the turbine than the type described above. The reason being that this type of turbine has a centrifugal pump effect such that the pressure drop across the turbine for a given gallonage of water is an inverse function of the r.p.m. that the turbine is rotating. As the turbine spins faster, due to light loading, the pressure drop across the turbine increases. As the load on the turbine is increased, the r.p.m. drops off, and the pressure drop across the turbine decreases. In other words, an inverse relationship exists between the load and the turbine pressure drop. Because of the very high pressure drop which occurs across the radial turbine when the load is light at the first part of the run, a bypass valve must be used. In tests, pressure drops in excess of 50 pounds per square inch have been recorded, when the bypass is closed and the turbine is unloaded. Any excess pressure drop across the turbine increases pumping costs considerably. For example, an additional 10 pounds per square inch pressure drop across the turbine system at a flow rate of 600 gallons per minute and a pump efficiency of 70%, would require an additional 5 brake horsepower at the pump.
Another problem with this type of turbine and bypass method of governor regulation is the amount of aperture or opening of the bypass valve which is quite critical. If the valve is set too far open, the torque of the turbine will be insufficient to keep the machine moving, after the hose pull increases. When the machine stalls in the field, crop damage will result. If the valve is set too far closed, pumping costs will be increased and/or less water will be delivered to the nozzle of the sprinkler and thus affecting the pattern. In order to maintain linear velocity through a field, the turbine must decrease its r.p.m. as the cable builds up on the winch drum. The operator is expected to use the trial and error method and balance bypass setting and mechanical drive leverage or gearing to achieve linear motion throughout the field and at the same time to acquire the desired speed. This is quite difficult to achieve and is a problem with such systems.
Another problem with the above system is that if the machine is properly calibrated for a given gallonage and field condition, it must be re-calibrated for either a gallonage or field condition change.
Another common problem is that different turbine sizes are required for different gallonage ranges. For example, one turbine size would be used for a range of 200 to 400 gallons per minute and a different size turbine would be used for the 400 to 600 gallons per minute range. This obviously limits the use to which one given sprinkler machine can be put and is quite undesirable.
Known prior art patents which may be pertinent to this invention are listed as follows:
1,142,448 H. L. Lord June 8, 1915 2,958,470 H. L. Giwosky Nov. 1, 1960 3,489,352 R. E. Diggs Jan. 13, 1970 3,583,636 J. J. Lacey June 8, 1971 3,687,372 N. P. Badcock Aug. 29, 1972 3,841,561 E. H. Lacey Oct. 15, 1974